The boat shaped scaphoid bone in the human wrist is the largest bone of the proximal row of the carpus on the lateral (radial) side, articulating with the radius, lunate, capitate, trapezium, and trapezoid. The scaphoid is surrounded on 80% of its surface by joint fluid containing fibrinolysin, a substance that dissolves blood clots.
The scaphoid is frequently fractured in young adults through the mid-portion, or xe2x80x9cwaistxe2x80x9d of the bone. Because blood clots are necessary for the healing of bone fractures, the substantial presence of fibrinolysin around the scaphoid inhibits healing of a fracture of that bone unless the fracture fragments are in sufficiently good apposition that joint fluid is prevented from entering the fracture site. Failure to properly fix the bone fragments into apposition will result in a non-union because of the presence in the fracture site of joint fluid.
In addition to an undesirable non-union, resulting from poor apposition, a fracture of the scaphoid through its waist often leads to avascular necrosis or death of the distal pole of the bone. This is because the blood supply to the bone is chiefly through the distal pole and an unhealed fracture at the bone waist cuts off the blood supply to the proximal pole, resulting eventually in severe arthritis and deformity of the wrist.
The traditional conservative treatment of a fractured scaphoid includes the application of a cast to the hand and thumb with the hand in radial deviation in an effort to oppose the fracture ends of the bone. Surgical intervention to fix the scaphoid bone typically includes the use of a screw that requires the expertise of a hand surgeon specialist, and a tedious and difficult surgical exposure.
The percutaneous method and the device of the present invention will allow a less experienced hand surgeon or an orthopedist to fix a scaphoid fracture with a cannular screw. Such simplification of the procedure leads to good apposition of the bone fragments and an overall improved result, including the minimization of surgical exposure of the wrist.
The present invention provides a simple percutaneous method that incorporates a novel appliance to promote the procedure. The essence of the method is to accurately resolve the required course of a fixation device, such as a cannular screw, and to be able to implant the device along the desired course.
The scaphoid bone is disposed in the wrist at a compound angle that is demonstrated only with an anterior-posterior x-ray and a lateral x-ray of the wrist. Even with the assistance of these x-rays, it is difficult to insert a fixation device that will follow the desired course into the scaphoid bone without substantial surgical intervention, accompanied by possible multiple attempts, or without the aid of an alignment jig, such as the one of the present invention. The apparatus of the present invention comprises a clamp or vise-like device having a pair of opposed relatively movable jaws between which the wrist containing the fractured scaphoid is inserted. Upon closing the jaws of the vise over the dorsal and palmar sides of the wrist, it is held in position so that A-P and lateral view x-rays may be taken. From these x-rays, the desired course of a fixation device may be resolved, including visualization of the angle of the scaphoid, as shown on the A-P view, and its vertical angulation, as shown on the lateral view. Once the course is determined, the single one of a plurality of bore holes in the lower jaw of the vise that is most closely aligned with the desired course is chosen for aligning and positioning a guide wire. Using the chosen bore to support and direct the guide wire, the wire is drilled through skin and subcutaneous tissue into the scaphoid bone, along the direction and at the angle imposed by the aligning bore.
Once the guide wire is drilled into the bone, the wrist is removed from the clamping vise. A small longitudinal incision is made in the tissue on either side of the guide wire and that tissue is then spread in order to accommodate the bit of a drill and the cannular screw that will be inserted into the bone.
A cannular drill bit is passed over the guide wire and a hole coaxial with the wire is drilled to terminate near the proximal end of the scaphoid bone. Following removal of the drill, a cannular lag screw of appropriate length is passed over the guide wire and screwed into the bone, bringing the fracture fragments snugly together in good apposition. The spread tissue is allowed to retract, the guide wire is removed and the incision is closed with a few sutures.
The bone apposition achieved by the accurately placed and well fitted cannular screw prevents joint fluid from entering the fracture site and dissolving the blood clots that are necessary for bone union.